This invention relates to tools for removing studs from a nuclear reactor vessel and particularly to such tools utilizing automated mechanisms and weight supporting devices.
In nuclear reactors well known in the art, the reactor comprises a core of fuel assemblies having fuel elements containing nuclear fuel which produce heat in a commonly understood fashion. The core is disposed within a reactor vessel designed to contain radioactive material that has an inlet and an outlet for circulating a coolant such as water in heat transfer relationship with the fuel assemblies. A closure head is located on the top of the reactor vessel and is usually bolted thereto by a plurality of studs that extend through the closure head and into the reactor vessel so as to seal the radioactive material in the reactor vessel. The reactor coolant that has been circulated through the reactor vessel transfers the heat produced by the core to steam generating equipment for the production of heat in a conventional manner. After a period of reactor operation, the fuel assemblies in the core become depleted and must be replaced with fresh ones in a process generally referred to as refueling. During the refueling of the reactor it is necessary to remove the closure head so that the fuel assemblies of the core may be accessed. In order to remove the closure head, it is first necessary to remove the studs which hold the closure head to the reactor vessel. Of course, once the refueling operation has been completed the closure head must be again fastened to the reactor vessel by means of the studs that were removed. There are many methods known in the art for so removing these studs; however, those methods have disadvantages which render them unsatisfactory.
One method known in the art for removing the studs from a reactor vessel closure head is to manually unscrew the studs by the use of strap wrenches. When the closure head studs have thus been unscrewed a lifting bolt may be attached to the closure head stud so that an overhead crane may lift and remove the closure head studs. Once the closure head studs have been removed, an overhead crane may be utilized to lift and remove the closure head so that access may be had to the fuel assemblies in the reactor core. After the refueling process has been completed, this process is reversed resulting in the closure head being bolted to the reactor vessel. While the process can be completed in this manner, it requires the use of several working personnel for approximately twenty hours. The length of time involved in such a process substantially delays the refueling process. Furthermore, because the working personnel must be stationed in a relatively high radiation exposure area during the stud removal and insertion process, additional personnel are needed in order to minimize the radiation exposure to any particular person.
Therefore, what is needed is an apparatus that can quickly remove or insert the reactor closure head studs without damaging them.